Bone anchors can be used in orthopedic surgery to fix bone during healing, fusion, or other processes. In spinal surgery, for example, bone anchors can be used to secure a spinal fixation element to one or more vertebrae to rigidly or dynamically stabilize the spine.
In a conventional procedure for coupling a bone anchor to bone, access to the bone is obtained, for example by forming a skin incision and resecting soft tissue disposed over the bone or by using a minimally-invasive technique. An insertion needle with a stylet disposed therein, sometimes referred to as a Jamshidi needle, is then driven into the bone to establish the trajectory for a bone opening. Next, the stylet is removed and a guidewire is inserted through the needle. The needle is then withdrawn over the guidewire, leaving the guidewire in place. A cannulated tap is then advanced over the guidewire and driven into the bone to enlarge the bone opening into a pilot hole for the bone anchor. Thereafter, the tap is withdrawn over the guidewire, again leaving the guidewire in place within the bone opening. A cannulated bone anchor is then advanced over the guidewire and driven into the bone opening. Finally, the guidewire is removed and one or more fixation elements are coupled to the bone anchor.
The conventional procedure detailed above suffers from a number of disadvantages. For example, the process involves several steps which can be time-consuming and cumbersome, particularly where a number of bone anchors are being installed. In addition, many of these steps (e.g., advancing the needle, advancing the guidewire, advancing the tap, and advancing the bone anchor) are done with fluoroscopic guidance to confirm the correct trajectory and insertion depth. The steps of removing the needle and removing the tap can also cause the guidewire to dislodge from the bone opening, requiring the process to be started anew. Further still, advancing the anchor or advancing the tap can inadvertently cause the guidewire to advance within the bone opening, potentially damaging delicate anatomical structures disposed in proximity to the bone. Advancing the anchor or advancing the tap can also cause the guidewire to become kinked, making removal of the guidewire very difficult. Accordingly, a need exists for improved bone anchors and associated instrumentation and methods.